A fiber-reinforced composite material composed of reinforcing fibers and a matrix resin has advantages, such as light weight, nigh strength, high modulus, etc., and is widely applied in aircrafts, sports and leisure, and general industries. This fiber-reinforced composition material is frequently produced via a prepreg in which the reinforcing fibers and the matrix resin are integrated with each other in advance.
The fiber-reinforced composite material that is produced by laminating and forming a prepreg having reinforcing fibers impregnated with a matrix resin generally includes a resin layer composed of the matrix resin between the respective fiber layers laminated. In general, the matrix resin used for the fiber-reinforced composite material is low in conductivity, and therefore, even if a fiber having conductivity is used for the reinforcing fibers, there is encountered such a problem that the conductivity in the thickness direction of the fiber-reinforced composite material is largely impaired by the resin layer between the fiber layers.
As a method of improving the interlayer conductivity, there are proposed a method of blending a metal particle in a resin composition constituting a prepreg (see PTL 1) and a method of blending a carbon particle in a resin composition constituting a prepreg (see PTL 2). In these methods, a large quantity of a conductive material particle is added in order to improve conductivity. But, since such a conductive material particle is low in adhesive properties to the resin, it is liable to become a starting point of fracture in the obtained fiber-reinforced composite material, whereby mechanical characteristics of the composite material are worsened. In addition, in prepreg production, such a conductive material particle largely thickens a resin composition to be impregnated in reinforcing fibers. For that reason, productivity of the prepreg or formability of the composite material is largely impaired. Since the composite material to be produced using such a prepreg involves various faults, such as a void, etc., there is encountered such a problem that mechanical characteristics, such as impact resistance, etc., are markedly worsened.
As a method of making both the impact resistance and the conductivity compatible with each other, for example, PTL 3 proposes a method of partly blending a resin layer of a fiber-reinforced composite material with a conductive particle having an equal diameter to a thickness of the resin layer. However, in this method, a blending amount of the conductive particle is small, so that there is a restriction in improving the conductivity. Furthermore, since the conductive particles are nonuniformly dispersed, there is encountered such a problem that scattering is caused in volume resistivity as an indicator of the conductivity.